Abstract Detail

An experimental approach to understanding the role of flooding in riparian plant community composition.

Riparian plant communities are often stated to be highly diverse. There are many potential drivers of this diversity, one of which is the hydrological dynamics of the habitat, including the role of flood events and disturbance in governing community dynamics and assembly. A flood event has many simultaneous effects on riparian vegetation. Plants experience submergence under water and associated oxygen deprivation, and may be damaged or uprooted due to scouring from fast-flowing water. They may also become coated in or buried under any sediments deposited under the floodwaters. At the same time, sediment deposition may also introduce nutrients to the riparian zone and aid the growth of riparian vegetation. In the field, it is difficult to untangle how each of these simultaneous effects of a flood affect riparian plant communities, or to identify whether any of them are the primary mechanism in determining the composition of these communities by excluding species that cannot tolerate flooding conditions. To examine the individual effects of multiple aspects of a flood event, a greenhouse experiment was conducted to test the effects of submergence, burial under sediments, and nutrient addition on the survival and growth of six herbaceous plant species. Species were chosen based on field observations of plant communities in the northeastern United States; three species were selected that were common in riparian zones, and three that were common in nearby upland areas but rarely or never observed in riparian zones. Riparian and upland species were chosen to represent pairs from each of three plant families: Asteraceae, Lamiaceae, and Polygonaceae. All but one of these species demonstrated increased growth in the nutrient addition treatment. Each of the riparian species had a high rate of survival under submergence conditions, but differed in their responses to burial under sediments. All upland species, conversely, performed poorly under burial conditions. The results of this experiment suggest that burial under sediments may play a primary role in excluding these three upland species from nearby riparian habitats, as they are unable to tolerate those conditions. Additionally, the three riparian species largely appear to tolerate rather than thrive under submergence and burial conditions, generally not demonstrating higher growth or survivorship in those treatments than in a control treatment experiencing only daily watering. These results provide initial insights into the mechanisms by which floods may influence riparian plant community composition and excluding some species that cannot tolerate those conditions.

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1 - Applied Biomathematics, 100 North Country Road, East Setauket, NY, 11733, United States